The present invention relates in general to heavy cyclical centrifugal machines and, more particularly, to a method for adjusting automatically an infeed gate supplying charge materials to the rotating centrifugal baskets of such machines so as to control the thicknesses of charge walls being formed along the inner sidewalls of the rotating centrifugal baskets. While the present invention is generally applicable to such machines, it will be described herein with reference to heavy cyclical centrifugal machines used for manufacturing and refining sugar.
A problem encountered when operating heavy cyclical centrifugal machines of the type used to manufacture and refine sugar is the inaccurate loading of the centrifugal baskets of the machines. These baskets should be fully loaded to their maximum capacities to maximize the productivity of the machines. Unfortunately, underloading the baskets results in reduced production and, when striving for maximum loading, the baskets are often overloaded so that charge material is lost from the basket resulting in waste even though production is increased. Variations in the loading properties of the charge material, massecuite for sugar manufacture and refining, can effect the efficiency of cycle to cycle centrifugal processing. These variations often occur from one batch of charge material to another and even occur between different portions of a single batch of charge material. Since these variations in loading properties are difficult or impossible to control, it has been an ongoing goal in the industry to control the loading operations of centrifugal machines such that the machines operate with maximum charge in spite of the charge material variations.
To control loading a centrifugal machine, measurements of the volume of the charge as it is being loaded into the machines have been made. For example, mechanical charge wall thickness measuring devices have been used to determine the thickness of the charge wall and thereby the volume of material in the charge basket of a machine, see U.S. Pat. Nos. 2,727,630; 3,011,641; 3,079,046; and, 3,141,846. A capacitance probe has been used also to determine wall thickness and hence the volume of material in the charge basket of a centrifugal machine, see U.S. Pat. No. 4,229,298. The mechanical and capacitance charge wall thickness measuring devices have been used with a variety of loading gates and loading gate control processes.
For example, the loading gate may be progressively closed as the charge measuring device indicates progressively increasing charge thickness in the centrifugal basket. When the charge wall approaches the desired thickness, the loading gate has moved to and is maintained at a pinched or largely closed position. When the final wall thickness is actually reached, the loading gate is quickly closed so that only a limited amount of material can flow into the basket as it closes from its pinched position to its fully closed position. The amount of material entering the basket during final closure of the loading gate from its pinched position to its fully closed position is insufficient to appreciably deviate from the desired final charge volume.
In another gate control process, the loading gate may be closed rapidly from its full open position to a pinched position and thereafter fully closed when the final wall thickness or volume has been reached. In yet another gate control process, the loading gate can be rapidly moved from its full open position to its fully closed position upon sensing the desired final wall thickness.
In still another gate control process which is currently enjoying substantial commercial success, when the charge wall approaches the desired thickness, the loading gate is rapidly moved to a pinched position which is a proportion of a selectable full open position from which it is to be closed, see U.S. Pat. No. 5,254,241 which is incorporated herein by reference. When the final wall thickness is actually reached, the loading gate is quickly closed so that only a limited amount of material can flow into the basket as it closes from its pinched position to its fully closed position.
The variety of loading gate control processes have been implemented, at least in part, to compensate for limitations in the measuring abilities of mechanical and capacitive charge wall thickness measuring devices. As should be expected, mechanical charge wall thickness measuring devices are prone to becoming fouled by the charge materials flowing into a basket of a centrifugal machine. While capacitive charge wall thickness measuring devices are a distinct improvement over mechanical devices, the sensitivity of capacitive devices is proportional to the inverse of the sensing distance so that their resolution is greatly diminished at larger measuring distances.
An ultrasonic probe has also been used to measure the charge wall thickness in a centrifugal machine, see U.S. Pat. No. 5,897,786 for a METHOD AND APPARATUS FOR DETERMINING THICKNESS OF A CHARGE WALL BEING FORMED IN A CENTRIFUGAL MACHINE which is incorporated herein by reference. The ultrasonic probe is mounted in the centrifugal machine within close proximity to a maximum charge wall which is to be formed within a charge basket of the centrifugal machine. The probe comprises a tubular member, which extends from an upper portion of an outer shell which surrounds the basket, into the basket. The probe is positioned to direct bursts of pulses of ultrasonic energy toward the inner surface of the basket and receive reflections or echoes of the pulses which are reflected from the charge wall building within the basket to monitor build up of a charge wall within the basket.
These ultrasonic probes are able to make highly accurate measurements over substantial distances and they are non-contact so that they have no wearing parts. In addition, the ultrasonic probes have highly linear measuring characteristics over their measurement range. The highly linear measuring characteristics of ultrasonic sensors make them ideal for measuring the thickness of a charge wall being formed in a centrifugal machine. Ultrasonic sensors have thus been used to replace mechanical and capacitive charge wall thickness measuring devices to operate gates in centrifugal machines using existing gate control processes. While the ultrasonic probes function admirably in this capacity, unfortunately, the existing gate control processes need to be improved to take full advantage of the ultrasonic probes.
Accordingly, there is a need for improved infeed gate control for supplying charge materials to the rotating centrifugal baskets of centrifugal machines so as to control more accurately and consistently the thicknesses of charge walls being formed along the inner sidewalls of the rotating centrifugal baskets regardless of the many variables which influence operation of such machines including, for example, consistency of the massecuite being used. Preferably, such improved gate control would enable the centrifugal machines to operate substantially independent of operator supervision so that a machine operator does not have to continually be present during operation of the machines.